Methods for determining meniscal size and shape and for devising treatment

ABSTRACT

The present invention relates to methods for determining meniscal size and shape for use in designing therapies for the treatment of various joint diseases. The invention uses an image of a joint that is processed for analysis. Analysis can include, for example, generating a thickness map, a cartilage curve, or a point cloud. This information is used to determine the extent of the cartilage defect or damage and to design an appropriate therapy, including, for example, an implant. Adjustments to the designed therapy are made to account for the materials used.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication 60/424,964 filed on Nov. 7, 2002.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

[0002] Certain aspects of the invention described below were made withUnited States Government support under Advanced Technology Program70NANBOH3016 awarded by the National Institute of Standards andTechnology (NIST). The United States Government may have rights incertain of these inventions.

FIELD OF THE INVENTION

[0003] The present invention relates to methods for determining meniscalsize and shape for use in designing therapies for the treatment ofvarious joint diseases. This method is then used to design an implant orarticular repair system for use in a joint.

BACKGROUND OF THE INVENTION

[0004] There are various types of cartilage, e.g., hyaline cartilage andfibrocartilage. Hyaline cartilage is found at the articular surfaces ofbones, e.g., in the joints, and is responsible for providing the smoothgliding motion characteristic of moveable joints. Articular cartilage isfirmly attached to the underlying bones and measures typically less than5 mm in thickness in human joints, with considerable variation dependingon the joint and more particularly the site within the joint. Inaddition, articular cartilage is aneural, avascular, and alymphatic

[0005] Adult cartilage has a limited ability of repair; thus, damage tocartilage produced by disease, such as rheumatoid arthritis and/orosteoarthritis, or trauma can lead to serious physical deformity anddebilitation. Furthermore, as human articular cartilage ages, itstensile properties change. Thus, the tensile stiffness and strength ofadult cartilage decreases markedly over time as a result of the agingprocess.

[0006] For example, the superficial zone of the knee articular cartilageexhibits an increase in tensile strength up to the third decade of life,after which it decreases markedly with age as detectable damage to typeII collagen occurs at the articular surface. The deep zone cartilagealso exhibits a progressive decrease in tensile strength with increasingage, although collagen content does not appear to decrease. Theseobservations indicate that there are changes in mechanical and, hence,structural organization of cartilage with aging that, if sufficientlydeveloped, can predispose cartilage to traumatic damage.

[0007] Once damage occurs, joint repair can be addressed through anumber of approaches. The use of matrices, tissue scaffolds or othercarriers implanted with cells (e.g., chondrocytes, chondrocyteprogenitors, stromal cells, mesenchymal stem cells, etc.) has beendescribed as a potential treatment for cartilage and meniscal repair orreplacement. See, also, International Publications WO 99/51719 toFofonoff, published Oct. 14, 1999; WO01/91672 to Simon et al., publishedDec. 6, 2001; and WO01/17463 to Mannsmann, published Mar. 15, 2001; U.S.Pat. No. 6,283,980 B1 to Vibe-Hansen et al., issued Sep. 4, 2001, U.S.Pat. No. 5,842,477 to Naughton issued Dec. 1, 1998, U.S. Pat. No.5,769,899 to Schwartz et al. issued Jun. 23, 1998, U.S. Pat. No.4,609,551 to Caplan et al. issued Sep. 2, 1986, U.S. Pat. No. 5,041,138to Vacanti et al. issued Aug. 29, 1991, U.S. Pat. No. 5,197,985 toCaplan et al. issued Mar. 30, 1993, U.S. Pat. No. 5,226,914 to Caplan etal. issued Jul. 13, 1993, U.S. Pat. No. 6,328,765 to Hardwick et al.issued Dec. 11, 2001, U.S. Pat. No. 6,281,195 to Rueger et al. issuedAug. 28, 2001, and U.S. Pat. No. 4,846,835 to Grande issued Jul. 11,1989. However, clinical outcomes with biologic replacement materialssuch as allograft and autograft systems and tissue scaffolds have beenuncertain since most of these materials cannot achieve a morphologicarrangement or structure similar to or identical to that of normal,disease-free human tissue it is intended to replace. Moreover, themechanical durability of these biologic replacement materials remainsuncertain.

[0008] Usually, severe damage or loss of cartilage is treated byreplacement of the joint with a prosthetic material, for example,silicone, e.g. for cosmetic repairs, or suitable metal alloys. See,e.g., U.S. Pat. No. 6,443,991 B1 to Running issued Sep. 3, 2002, U.S.Pat. No. 6,387,131 B1 to Miehlke et al. issued May 14, 2002; U.S. Pat.No. 6,383,228 to Schmotzer issued May 7, 2002; U.S. Pat. No. 6,344,059B1 to Krakovits et al. issued Feb. 5, 1002; U.S. Pat. No. 6,203,576 toAfriat et al. issued Mar. 20, 2001; U.S. Pat. No. 6,126,690 to Ateshianet al. issued Oct. 3, 2000; U.S. Pat. No. 6,013,103 to Kaufman et al.issued Jan. 11, 2000. Implantation of these prosthetic devices isusually associated with loss of underlying tissue and bone withoutrecovery of the full function allowed by the original cartilage and,with some devices, serious long-term complications associated with theloss of significant amounts of tissue and bone can include infection,osteolysis and also loosening of the implant.

[0009] As can be appreciated, joint arthroplasties are highly invasiveand require surgical resection of the entire, or a majority of the,articular surface of one or more bones involved in the repair. Typicallywith these procedures, the marrow space is fairly extensively reamed inorder to fit the stem of the prosthesis within the bone. Reaming resultsin a loss of the patient's bone stock and over time subsequentosteolysis will frequently lead to loosening of the prosthesis. Further,the area where the implant and the bone mate degrades over timerequiring the prosthesis to eventually be replaced. Since the patient'sbone stock is limited, the number of possible replacement surgeries isalso limited for joint arthroplasty. In short, over the course of 15 to20 years, and in some cases even shorter time periods, the patient canrun out of therapeutic options ultimately resulting in a painful,non-functional joint.

[0010] U.S. Pat. No. 6,206,927 to Fell, et al., issued Mar. 27, 2001,and U.S. Pat. No. 6,558,421 to Fell, et al., issued May 6, 2003,disclose a surgically implantable knee prosthesis that does not requirebone resection. This prosthesis is described as substantially ellipticalin shape with one or more straight edges. Accordingly, these devices arenot designed to substantially conform to the actual shape (contour) ofthe remaining cartilage in vivo and/or the underlying bone. Thus,integration of the implant can be extremely difficult due to differencesin thickness and curvature between the patient's surrounding cartilageand/or the underlying subchondral bone and the prosthesis.

[0011] Interpositional knee devices that are not attached to both thetibia and femur have been described. For example, Platt et al. (1969)“Mould Arthroplasty of the Knee,” Journal of Bone and Joint Surgery51B(1):76-87, describes a hemi-arthroplasty with a convex undersurfacethat was not rigidly attached to the tibia.

[0012] U.S. Pat. No. 4,502,161 to Wall issued Mar. 5, 1985, describes aprosthetic meniscus constructed from materials such as silicone rubberor Teflon with reinforcing materials of stainless steel or nylonstrands. U.S. Pat. No. 4,085,466 to Goodfellow et al. issued Mar. 25,1978, describes a meniscal component made from plastic materials.Reconstruction of meniscal lesions has also been attempted withcarbon-fiber-polyurethane-poly (L-lactide). Leeslag, et al., Biologicaland Biomechanical Performance of Biomaterials (Christel et al., eds.)Elsevier Science Publishers B.V., Amsterdam. 1986. pp. 347-352.Reconstruction of meniscal lesions is also possible with bioresorbablematerials and tissue scaffolds.

[0013] However, currently available devices do not always provide idealalignment with the articular surfaces and the resultant joint congruity.Poor alignment and poor joint congruity can, for example, lead toinstability of the joint. In the knee joint, instability typicallymanifests as a lateral instability of the joint.

[0014] Thus, there remains a need for methods that recreate natural ornear natural relationships between two articular surfaces of the joint(such as the femoral condyle and the tibial plateau).

SUMMARY OF THE INVENTION

[0015] In one aspect, when the meniscus is present in the subject, theinvention includes measuring the dimensions and/or shape, parameters ofthe meniscus. Such dimensions and parameters include, for example, butare not limited to, the maximum anterior-posterior distance of themeniscus, the maximum medial-lateral distance of the meniscus, the sizeor area of the meniscal attachment(s), the maximum length of theanterior horn, the maximum and minimum height of the anterior horn, themaximum and minimum height of the body, the maximum and minimum heightof the posterior horn, the maximum height and minimum height of themeniscus, the maximum and minimum width of the anterior horn, themaximum and minimum width of the body, the maximum and minimum width ofthe posterior horn, meniscal radii and angles at various locations.These measurements can then be used to design therapies for thetreatment of joint diseases. These treatments can include, for example,meniscal repair systems, cartilage repair systems, articular repairsystems and arthroplasty systems and they can consist of, for example,biologic materials, tissue scaffolds, plastic, metal or metal alloys, orcombinations thereof. Therapies can be custom-made, typically utilizingat least one or more of these measurements. Alternatively, a pre-made,“off-the-shelf” component closely matching at least one or more of thesemeasurements can be selected.

[0016] In another aspect, the invention includes measuring thedimensions and/or shape parameters of the contralateral meniscus. Suchdimensions and parameters include, for example, but are not limited to,the maximum anterior-posterior distance of the meniscus, the maximummedial-lateral distance of the meniscus, the size or area of themeniscal attachment(s), the maximum length of the anterior horn, themaximum length of the body, the maximum length of the posterior horn,the maximum and minimum height of the anterior horn, the maximum andminimum height of the body, the maximum and minimum height of theposterior horn, the maximum height and minimum height of the meniscus,the maximum and minimum width of the anterior horn, the maximum andminimum width of the body, the maximum and minimum width of theposterior horn, meniscal radii, and angles at various locations.

[0017] In one embodiment, the meniscus of the opposite compartment canbe used to create a mirror image of the meniscus on the diseased side.These measurements can then be used to determine meniscal size and/orshape in designing treatments for the diseased joint. These treatmentscan include, for example, meniscal repair systems, cartilage repairsystems, articular repair systems and arthroplasty systems and they canconsist of, for example, biologic materials, tissue scaffolds, plastic,metal or metal alloys or combinations thereof. Therapies can becustom-made, typically utilizing at least one or more of thesemeasurements. Alternatively, a pre-made, “off-the-shelf” componentmatching or closely matching at least one or more of these measurementscan be selected.

[0018] In yet another embodiment, the 3D geometry of the meniscus on theaffected site can be derived from measurements from neighboringarticular surfaces and structures to recreate the shape and size of thediseased meniscus. Such measurements include, for example, but are notlimited to, tibial bone dimensions, such as maximum anterior-posteriordistance, maximum medial-lateral distance, maximum distance from thetibial spine to the edge, width of the tibial spines, height of thetibial spines, area of tibial plateau occupied by tibial spines, depthof tibial plateau, 2D and 3D shape of tibial plateau; femoral condylebone dimensions, such as maximum anterior-posterior distance, maximumsuperior-inferior distance, maximum medial-lateral distance, maximumdistance from the trochlea to the medial or lateral edge; width anddepth of intercondylar notch, curvature at select regions along thefemoral condyle, 2D and 3D shape.

[0019] In yet another aspect, when applied to the knee joint theinvention includes one or more of the following measurements: (1) tibialbone dimensions, for example, maximum anterior-posterior distance,maximum medial-lateral distance, maximum distance from the tibial spineto the edge, width of the tibial spines, height of the tibial spines,area of tibial plateau occupied by tibial spines, depth of tibialplateau, 2D and 3D shape of tibial plateau; (2) tibial cartilagedimensions, including thickness and shape; (3) femoral condyle bonedimensions, for example, maximum anterior-posterior distance, maximumsuperior-inferior distance, maximum medial-lateral distance, maximumdistance from the trochlea to the medial or lateral edge; width anddepth of intercondylar notch, curvature at select regions along thefemoral condyle, 2D and 3D shape; and (4) femoral cartilage measurementsincluding thickness and shape. These measurements can then be used toestimate meniscal size and/or shape for the treatment of joint diseases.These treatments can include, for example, meniscal repair systems,cartilage repair systems, articular repair systems and arthroplastysystems and it can consist of, for example, biologic materials, tissuescaffolds, plastic, metal or metal alloys, or combinations thereof.Therapies can be custom-made, typically utilizing at least one or moreof these measurements. Alternatively, a pre-made, “off-the-shelf”component closely matching at least one or more of these measurementscan be selected.

[0020] In a further aspect, meniscal measurements are taken from areference population possessing normal or near normal menisci. Meniscalmeasurements can include, but are not limited to, for example, themaximum anterior-posterior distance of the meniscus, the maximummedial-lateral distance of the meniscus, the size or area of themeniscal attachment(s), the maximum length of the anterior horn, themaximum length of the body, the maximum length of the posterior horn,the maximum and minimum height of the anterior horn, the maximum andminimum height of the body, the maximum and minimum height of theposterior horn, the maximum height and minimum height of the meniscus,the maximum and minimum width of the anterior horn, the maximum andminimum width of the body, the maximum and minimum width of theposterior horn, meniscal radii and angles at various locations.

[0021] Additional non-meniscal measurements can also be taken using thesame reference population and may include one or more of the following:(1) tibial bone dimensions, for example, maximum anterior-posteriordistance, maximum medial-lateral distance, maximum distance from thetibial spine to the edge, width of the tibial spines, height of thetibial spines, area of tibial plateau occupied by tibial spines, depthof tibial plateau, 2D and 3D shape of tibial plateau; (2) tibialcartilage dimensions including thickness and shape; (3) femoral condylebone dimensions, for example, maximum anterior-posterior distance,maximum superior-inferior distance, maximum medial-lateral distance,maximum distance from the trochlea to the medial or lateral edge, widthand depth of the intercondylar notch, curvature at select regions alongthe femoral condyle, 2D and 3D shape, (4) femoral cartilage measurementsincluding thickness and shape; (5) measuring the patellar bonedimensions; (6) measuring the patellar cartilage dimensions includingthickness and shape; and/or (7) measuring the size, length or shape ofligamentous structures such as the cruciate ligaments.

[0022] The size and/or shape of the menisci in the reference populationcan then be correlated to one or more of the additional non-meniscalmeasurements. Once a correlation is established, the bone and/orcartilage and/or ligamentous dimensions with the highest correlation tomeniscal size and/or shape can be used to predict meniscal size and/orshape in designing therapies for persons suffering from joint disease.The data from the reference population is typically stored in a databasewhich can be periodically or continuously updated. Using thisinformation, therapies can be devices which include, for example,meniscal repair systems, cartilage repair systems, articular repairsystems and arthroplasty systems and they can consist of, for example,biologic materials, tissue scaffolds, plastic, metal or metal alloys, orcombinations thereof. Therapies can be custom-made, typically utilizingat least one or more of these measurements. Alternatively, a pre-made,“off-the-shelf” component closely matching at least one or more of thesemeasurements can be selected. For example, a meniscal repair system canbe selected utilizing this information. Alternatively, this informationcan be utilized in shaping an interpositional arthroplasty system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1A illustrates an example of a Placido disk of concentricallyarranged circles of light. FIG. 1B illustrates an example of a projectedPlacido disk on a surface of fixed curvature.

[0024]FIG. 2 shows a reflection resulting from a projection ofconcentric circles of light (Placido Disk) on each femoral condyle,demonstrating the effect of variation in surface contour on thereflected circles.

[0025]FIG. 3 illustrates an example of a 2D color-coded topographicalmap of an irregularly curved surface.

[0026]FIG. 4 illustrates an example of a 3D color-coded topographicalmap of an irregularly curved surface.

[0027]FIG. 5 illustrates surface registration of MRI surface and adigitized surface using a laser scanner. The illustration to the leftshows the surface before registration and the illustration to the rightshows the surface after registration.

[0028]FIG. 6 is a reproduction of a three-dimensional thickness map ofthe articular cartilage of the distal femur. Three-dimensional thicknessmaps can be generated, for example, from ultrasound, CT or MRI data.Dark holes within the substances of the cartilage indicate areas of fullthickness cartilage loss.

[0029]FIG. 7 illustrates the cartilage surface of a medial femoralcondyle from a sagittal scan (blue) and a coronal scan (red).

[0030]FIG. 8A illustrates an axial view of a meniscus; FIG. 8Billustrates a sagittal view of the meniscus; and FIG. 8C illustrates acoronal view of the meniscus.

[0031]FIG. 9A illustrates a sagittal view of the tibia; and FIG.illustrates a coronal view of the tibia.

[0032]FIG. 10A illustrates a sagittal view of the femur; and FIG. 10Billustrates a coronal view of the femur.

[0033] FIGS. 11A-C illustrate a chart showing the tibial cartilagesurface and superior meniscal surface combined after extraction from acoronal FSE, and a meniscal surface scaled to account for compressionunder loading conditions. From the information is derived thecross-section of the implant, FIG. 11C.

[0034]FIG. 12 illustrates a point cloud of an implant surface (yellow)that approximates smooth surface patch (brown).

[0035]FIGS. 13A and B are views of an implant suitable for use on acondyle of the femur shown from the inferior and superior surfaceviewpoints, respectively.

[0036]FIG. 14 is a view of an implant suitable for a portion of thetibial plateau in the knee.

[0037] FIGS. 15A-D are views of an implant suitable for the hip.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The following description is presented to enable any personskilled in the art to make and use the invention. Various modificationsto the embodiments described will be readily apparent to those skilledin the art, and the generic principles defined herein can be applied toother embodiments and applications without departing from the spirit andscope of the present invention as defined by the appended claims. Thus,the present invention is not intended to be limited to the embodimentsshown, but is to be accorded the widest scope consistent with theprinciples and features disclosed herein. To the extent necessary toachieve a complete understanding of the invention disclosed, thespecification and drawings of all issued patents, patent publications,and patent applications cited in this application are incorporatedherein by reference.

[0039] As will be appreciated by those of skill in the art, the practiceof the present invention employs, unless otherwise indicated,conventional methods of x-ray imaging and processing, x-raytomosynthesis, ultrasound including A-scan, B-scan and C-scan, computedtomography (CT scan), magnetic resonance imaging (MRI), opticalcoherence tomography, single photon emission tomography (SPECT) andpositron emission tomography (PET) within the skill of the art. Suchtechniques are explained fully in the literature and need not bedescribed herein. See, e.g., X-Ray Structure Determination: A PracticalGuide, 2nd Edition, editors Stout and Jensen, 1989, John Wiley & Sons,publisher; Body CT: A Practical Approach, editor Slone, 1999,McGraw-Hill publisher; X-ray Diagnosis: A Physician's Approach, editorLam, 1998 Springer-Verlag, publisher; and Dental Radiology:Understanding the X-Ray Image, editor Laetitia Brocklebank 1997, OxfordUniversity Press publisher.

[0040] The present invention solves the need for methods to recreatenatural or near natural relationships between two articular surfaces byproviding methods for determining meniscal size and shape. Meniscal sizeand shape can be useful in designing therapies for the treatment ofjoint diseases including, for example, meniscal repair, meniscalregeneration, and articular repair therapies.

[0041] I. Assessment of Joints

[0042] The methods and compositions described herein can be used totreat defects resulting from disease of the cartilage (e.g.,osteoarthritis), bone damage, cartilage damage, trauma, and/ordegeneration due to overuse or age. The invention allows, among otherthings, a health practitioner to evaluate and treat such defects.

[0043] As will be appreciated by those of skill in the art, size,curvature and/or thickness measurements can be obtained using anysuitable technique. For example, one dimensional, two dimensional,and/or three dimensional measurements can be obtained using suitablemechanical means, laser devices, electromagnetic or optical trackingsystems, molds, materials applied to the articular surface that hardenand “memorize the surface contour,” and/or one or more imagingtechniques known in the art. Measurements can be obtained non-invasivelyand/or intraoperatively (e.g., using a probe or other surgical device).As will be appreciated by those of skill in the art, the thickness ofthe repair device can vary at any given point depending upon the depthof the damage to the cartilage and/or bone to be corrected at anyparticular location on an articular surface.

[0044] A. Imaging Techniques

[0045] As will be appreciated by those of skill in the art, imagingtechniques suitable for measuring thickness and/or curvature (e.g., ofcartilage and/or bone) or size of areas of diseased cartilage orcartilage loss include the use of x-rays, magnetic resonance imaging(MRI), computed tomography scanning (CT, also known as computerizedaxial tomography or CAT), optical coherence tomography, SPECT, PET,ultrasound imaging techniques, and optical imaging techniques. (See,also, International Patent Publication WO 02/22014 to Alexander, et al.,published Mar. 21, 2002; U.S. Pat. No. 6,373,250 to Tsoref et al.,issued Apr. 16, 2002; and Vandeberg et al. (2002) Radiology 222:430436).Contrast or other enhancing agents can be employed using any route ofadministration, e.g. intravenous, intra-articular, etc.

[0046] In certain embodiments, CT or MRI is used to assess tissue, bone,cartilage and any defects therein, for example cartilage lesions orareas of diseased cartilage, to obtain information on subchondral boneor cartilage degeneration and to provide morphologic or biochemical orbiomechanical information about the area of damage. Specifically,changes such as fissuring, partial or full thickness cartilage loss, andsignal changes within residual cartilage can be detected using one ormore of these methods. For discussions of the basic NMR principles andtechniques, see MRI Basic Principles and Applications, Second Edition,Mark A. Brown and Richard C. Semelka, Wiley-Liss, Inc. (1999). For adiscussion of MRI including conventional T1 and T2-weighted spin-echoimaging, gradient recalled echo (GRE) imaging, magnetization transfercontrast (MTC) imaging, fast spin-echo (FSE) imaging, contrast enhancedimaging, rapid acquisition relaxation enhancement (RARE) imaging,gradient echo acquisition in the steady state (GRASS), and drivenequilibrium Fourier transform (DEFT) imaging, to obtain information oncartilage, see Alexander, et al., WO 02/22014. Thus, in preferredembodiments, the measurements produced are based on three-dimensionalimages of the joint obtained as described in Alexander, et al., WO02/22014 or sets of two-dimensional images ultimately yielding 3Dinformation. Two-dimensional and three-dimensional images, or maps, ofthe cartilage alone or in combination with a movement pattern of thejoint, e.g. flexion—extension, translation and/or rotation, can beobtained. Three-dimensional images can include information on movementpatterns, contact points, contact zone of two or more opposing articularsurfaces, and movement of the contact point or zone during joint motion.Two and three-dimensional images can include information on biochemicalcomposition of the articular cartilage. In addition, imaging techniquescan be compared over time, for example to provide up-to-date informationon the shape and type of repair material needed.

[0047] Any of the imaging devices described herein can also be usedintra-operatively (see, also below), for example using a hand-heldultrasound and/or optical probe to image the articular surfaceintra-operatively.

[0048] B. Intraoperative Measurements

[0049] Alternatively, or in addition to, non-invasive imaging techniquesdescribed above, measurements of the size of an area of diseasedcartilage or an area of cartilage loss, measurements of cartilagethickness and/or curvature of cartilage or bone can be obtainedintraoperatively during arthroscopy or open arthrotomy. Intraoperativemeasurements may or may not involve actual contact with one or moreareas of the articular surfaces.

[0050] Devices suitable for obtaining intraoperative measurements ofcartilage or bone or other articular structures, and to generate atopographical map of the surface include but are not limited to, Placidodisks and laser interferometers, and/or deformable materials or devices.(See, for example, U.S. Pat. No. 6,382,028 to Wooh et al., issued May 7,2002; U.S. Pat. No. 6,057,927 to Levesque et al., issued May 2, 2000;U.S. Pat. No. 5,523,843 to Yamane et al. issued Jun. 4, 1996; U.S. Pat.No. 5,847,804 to Sarver et al. issued Dec. 8,1998; and U.S. Pat. No.5,684,562 to Fujieda, issued Nov. 4, 1997).

[0051]FIG. 1A illustrates a Placido disk of concentrically arrangedcircles of light. The concentric arrays of the Placido disk projectwell-defined circles of light of varying radii, generated either withlaser or white light transported via optical fiber. The Placido disk canbe attached to the end of an endoscopic device (or to any probe, forexample a hand-held probe) so that the circles of light are projectedonto the cartilage surface. FIG. 1B illustrates an example of a Placidodisk projected onto the surface of a fixed curvature. One or moreimaging cameras can be used (e.g., attached to the device) to capturethe reflection of the circles. Mathematical analysis is used todetermine the surface curvature. The curvature can then, for example, bevisualized on a monitor as a color-coded, topographical map of thecartilage surface. Additionally, a mathematical model of thetopographical map can be used to determine the ideal surface topographyto replace any cartilage defects in the area analyzed.

[0052]FIG. 2 shows a reflection resulting from the projection ofconcentric circles of light (Placido disk) on each femoral condyle,demonstrating the effect of variation in surface contour on reflectedcircles.

[0053] Similarly a laser interferometer can also be attached to the endof an endoscopic device. In addition, a small sensor can be attached tothe device in order to determine the cartilage surface or bone curvatureusing phase shift interferometry, producing a fringe pattern analysisphase map (wave front) visualization of the cartilage surface. Thecurvature can then be visualized on a monitor as a color coded,topographical map of the cartilage surface. Additionally, a mathematicalmodel of the topographical map can be used to determine the idealsurface topography to replace any cartilage or bone defects in the areaanalyzed. This computed, ideal surface, or surfaces, can then bevisualized on the monitor, and can be used to select the curvature, orcurvatures, of the replacement cartilage.

[0054] One skilled in the art will readily recognize that othertechniques for optical measurements of the cartilage surface curvaturecan be employed without departing from the scope of the invention. Forexample, a 2-dimentional or 3-dimensional map, such as that shown inFIG. 3 and FIG. 4 can be generated.

[0055] Mechanical devices (e.g., probes) can also be used forintraoperative measurements, for example, deformable materials such asgels, molds, any hardening materials (e.g., materials that remaindeformable until they are heated, cooled, or otherwise manipulated).See, e.g., WO 02/34310 to Dickson et al., published May 2, 2002. Forexample, a deformable gel can be applied to a femoral condyle. The sideof the gel pointing towards the condyle can yield a negative impressionof the surface contour of the condyle. The negative impression can thenbe used to determine the size of a defect, the depth of a defect and thecurvature of the articular surface in and adjacent to a defect. Thisinformation can be used to select a therapy, e.g. an articular surfacerepair system. In another example, a hardening material can be appliedto an articular surface, e.g. a femoral condyle or a tibial plateau. Thehardening material can remain on the articular surface until hardeninghas occurred. The hardening material can then be removed from thearticular surface. The side of the hardening material pointing towardsthe articular surface can yield a negative impression of the articularsurface. The negative impression can then be used to determine the sizeof a defect, the depth of a defect and the curvature of the articularsurface in and adjacent to a defect. This information can then be usedto select a therapy, e.g. an articular surface repair system. In someembodiments, the hardening system can remain in place and form theactual articular surface repair system.

[0056] In certain embodiments, the deformable material comprises aplurality of individually moveable mechanical elements. When pressedagainst the surface of interest, each element can be pushed in theopposing direction and the extent to which it is pushed (deformed) cancorrespond to the curvature of the surface of interest. The device caninclude a brake mechanism so that the elements are maintained in theposition that conforms to the surface of the cartilage and/or bone. Thedevice can then be removed from the patient and analyzed for curvature.Alternatively, each individual moveable element can include markersindicating the amount and/or degree it is deformed at a given spot. Acamera can be used to intra-operatively image the device and the imagecan be saved and analyzed for curvature information. Suitable markersinclude, but are not limited to, actual linear measurements (metric orempirical), different colors corresponding to different amounts ofdeformation and/or different shades or hues of the same color(s).Displacement of the moveable elements can also be measured usingelectronic means.

[0057] Other devices to measure cartilage and subchondral boneintraoperatively include, for example, ultrasound probes. An ultrasoundprobe, preferably handheld, can be applied to the cartilage and thecurvature of the cartilage and/or the subchondral bone can be measured.Moreover, the size of a cartilage defect can be assessed and thethickness of the articular cartilage can be determined. Such ultrasoundmeasurements can be obtained in A-mode, B-mode, or C-mode. If A-modemeasurements are obtained, an operator can typically repeat themeasurements with several different probe orientations, e.g.mediolateral and anteroposterior, in order to derive a three-dimensionalassessment of size, curvature and thickness.

[0058] One skilled in the art will easily recognize that different probedesigns are possible using the optical, laser interferometry, mechanicaland ultrasound probes. The probes are preferably handheld. In certainembodiments, the probes or at least a portion of the probe, typicallythe portion that is in contact with the tissue, can be sterile.Sterility can be achieved with use of sterile covers, for examplesimilar to those disclosed in WO 99/08598A1 to Lang, published Feb. 25,1999.

[0059] Analysis on the curvature of the articular cartilage orsubchondral bone using imaging tests and/or intraoperative measurementscan be used to determine the size of an area of diseased cartilage orcartilage loss. For example, the curvature can change abruptly in areasof cartilage loss. Such abrupt or sudden changes in curvature can beused to detect the boundaries of diseased cartilage or cartilagedefects.

[0060] II. Segmentation of Articular Cartilage, Bone and Menisci

[0061] A semi-automated segmentation approach has been implemented basedon the live wire algorithm, which provides a high degree of flexibilityand therefore holds the potential to improve segmentation ofosteoarthritic cartilage considerably. Images are optionallypre-processed using a non-linear diffusion filter. The live wirealgorithm assigns a list of features to each oriented edge between twopixels (boundary element—bel) in an image. Using an individual costfunction for each feature, the feature values are converted into costvalues. The costs for each feature are added up by means of apredetermined weighting scheme, resulting in a single joint cost valuebetween 0 and 1 for each bel b that expresses the likelihood of b beingpart of the cartilage boundary. To determine the contour of a cartilageobject, the operator chooses a starting pixel P. Subsequently, thesystem calculates the least cost bel path from each image pixel to Pwith a dynamic programming scheme. When the operator selects anotherpixel, the system displays the calculated path from the current mouseposition to P in real time. This current path can be frozen as part ofthe cartilage contour by the operator. This way, the operator has toassemble the desired contour in each slice from a number of pieces(“strokes”).

[0062] The features of a bel b used with this segmentation technique arethe gray values left and right of b and the magnitude of the gray levelgradient across b.

[0063] As will be appreciated by those of skill in the art, all or aportion of the segmentation processes described can be automated asdesired. As will be appreciated by those of skill in the art, othersegmentation techniques including but not limited to thresholding, greylevel gradient techniques, snakes, model based segmentation, watershed,clustering, statistical segmentation, filtering including lineardiffusion filtering can be employed.

[0064] III. Validation of Cartilage Surface Segmentation

[0065] In order to validate the accuracy of the segmentation techniquefor the articular cartilage surface, the cartilage surface extractedfrom MRI scans can be compared with results obtained from segmentationof the joint surface data which is acquired, for example, using a laserscanner after specimen dissection. The resulting two surfaces from MRIand laser scan can be registered using the iterative closest pointmethod, and the distance between each point on the MRI surface to theregistered laser scan surface can be used to determine the accuracy ofthe MRI segmentation results. FIG. 5 shows the MRI and digitizedsurfaces before and after registration. The distance measurements forthe two specimens are shown in TABLE 1. TABLE 1 DISTANCE CALCULATIONSBETWEEN SEGMENTED MRI AND LASER DIGITIZED SURFACES (IN MM) MinimumMaximum Mean Standard Specimen Distance Distance Distance M Deviation σ1 3.60447e−05 2.10894 0.325663 0.312803 2 2.79092e−06 1.616828 0.2621310.234424

[0066] In this example, the data illustrate that the average errorbetween the segmented MRI surface and the laser scan surface is withinthe range of the resolution of the MRI scan. Thus, the segmentationapproach yields an accuracy within the given MRI scan parameters.

[0067] IV. Calculation and Visualization of Cartilage ThicknessDistribution

[0068] A suitable approach for calculating the cartilage thickness isbased on a 3D Euclidean distance transform (EDT). An algorithm by Saitoand Toriwaki can be used to achieve computationally very fast (less than10 sec for a 256×256×60 data set on a SGI O2) data processing. Thealgorithm functions by decomposing the calculation into a series of 3one-dimensional transformations and uses the square of the actualdistances. This process accelerates the analysis by avoiding thedetermination of square roots. For initialization, voxels on the innercartilage surface (ICS) are given a value of 0, whereas all othervoxels, including the ones on the outer cartilage surface (OCS) are setto 1.

[0069] First, for a binary input picture F={f_(ijk)} (1≦i≦L, 1, ≦j≦M,1≦k≦N) a new picture G={g_(ijk)} is derived using equation 1 (α, β, andγ denote the voxel dimensions). $\begin{matrix}{g_{ijk} = {\min\limits_{x}\left\{ {\left( {\alpha \left( {i - x} \right)} \right)^{2};{f_{xjk} = 0};{1 \leq x \leq L}} \right\}}} & \left\lbrack {{Eq}.\quad 1} \right\rbrack\end{matrix}$

[0070] Thus, each point is assigned the square of the distance to theclosest feature point in the same row in i-direction. Second, G isconverted into H={h_(ijk)} using equation 2. $\begin{matrix}{h_{ijk} = {\min\limits_{y}\left\{ {{g_{iyk} + \left( {\beta \left( {j - y} \right)} \right)^{2}};{1 \leq y \leq M}} \right\}}} & \left\lbrack {{Eq}.\quad 2} \right\rbrack\end{matrix}$

[0071] The algorithm searches each column in j-direction. According tothe Pythagorean theorem, the sum of the square distance between a point(i,j,k) and a point (i,y,k) in the same column, (β(j−y))², and thesquare distance between (i,y,k) and a particular feature point, g_(iyk),equals the square distance between the point (i,j,k) and that featurepoint. The minimum of these sums is the square distance between (i,j,k)and the closest feature point in the two-dimensional i-j-plane.

[0072] The third dimension is added by equation 3, which is the sametransformation as described in equation 2 for the k-direction.$\begin{matrix}{s_{ijk} = {\min\limits_{z}\left\{ {{h_{ijz} + \left( {\gamma \left( {k - z} \right)} \right)^{2}};{1 \leq z \leq N}} \right\}}} & \left\lbrack {{Eq}.\quad 3} \right\rbrack\end{matrix}$

[0073] After completion of the EDT, the thickness of the cartilage for agiven point (a,b,c) on the OCS equals the square root of s_(abc). Thisresults in a truly three-dimensional distance value determined normal tothe ICS. The x, y, and z position of each pixel located along thebone-cartilage interface is registered on a 3D map and thickness valuesare translated into color values. In this fashion, the anatomic locationof each pixel at the bone-cartilage interface can be displayedsimultaneously with the thickness of the cartilage for that givenlocation (FIG. 6).

[0074] As will be appreciated by those of skill in the art, othertechniques for calculating cartilage thickness can be applied, forexample using the LaPlace equation, without departing from the scope ofthe invention.

[0075] V. Calculation and Visualization of Cartilage CurvatureDistribution

[0076] Another relevant parameter for the analysis of articularcartilage surfaces is curvature. In a fashion similar to the thicknessmap, a set of curvature maps can be derived from the cartilage surfacedata that is extracted from the MRI.

[0077] A local bi-cubic surface patch is fitted to the cartilage surfacebased on a sub-sampling scheme in which every other surface point isused to generate a mesh of 5×5 point elements. Thus, before performingthe fit the density of the data is reduced in order to smooth the fittedsurface and to reduce the computational complexity.

[0078] After computation of the local bi-cubic surface fits, the unitnormal vectors {n} are implicitly estimated from the surface fit data.The corresponding curvature and its orientation are then given by:

κ_(i)=arc cos(n ₀ ·n _(i))|ds _(i) =dθ/ds _(i),

[0079] where n_(o) is the unit normal vector at the point (u,v) wherethe curvature is being estimated and n_(i) (i=1, . . . , 24) are theunit normal vectors at each one of the surrounding points in the 5×5local surface patch. FIG. 6 shows an example of the maximum principalcurvature maps (value and direction), estimated using the bi-cubicsurface patch fitting approach.

[0080] As will be appreciated by those of skill in the art, othertechniques, such as n-degree polynomial surface interpolation orapproximation, parametric surface interpolation or approximation anddifferent discrete curvature estimation methods for measuring curvatureor 3D shape can be applied.

[0081] VI. Fusion of Image Data from Multiple Planes

[0082] Recently, technology enabling the acquisition of isotropic ornear-isotropic 3-dimensional image data has been developed. However,most MRI scans are still acquired with a slice thickness that is 3 ormore times greater than the in-plane resolution. This leads tolimitations with respect to 3D image analysis and visualization. Thestructure of 3-dimensional objects cannot be described with the sameaccuracy in all three dimensions. Partial volume effects hinderinterpretation and measurements in the z-dimension to a greater extentthan in the x-y plane.

[0083] To address the problems associated with non-isotropic imageresolutions, one or more first scans S1 are taken in a first plane. Eachof the first scans are parallel to each other. Thereafter, one or moresecond scans S2 are taken with an imaging plane oriented to the firstscan S1 so that the planes intersect. For example, scans S1 can be in afirst plane while scans S2 are in a plane perpendicular to the firstplane. Additional scans in other planes or directions, e.g., S3, S4. . .Sn, can also be obtained in addition to the perpendicular scans orinstead of the perpendicular scans. S2, and any other scans, can havethe same in-plane resolution as S1. Any or all of the scans can alsocontain a sufficient number of slices to cover the entire field of viewof S1. In this scenario, two data volumes with information from the same3D space or overlapping 3D spaces can be generated.

[0084] Data can be merged from these two scans to extract the objects ofinterest in each scan independently. Further, a subsequent analysis cancombine these two segmented data sets in one coordinate system, as isshown in FIG. 6. This technique is helpful in outlining the boundariesof objects that are oriented parallel to the imaging plane of S1, buttherefore will be perpendicular to the imaging plane of S2.

[0085] For quantitative measurements, such as determining the cartilagevolume, it can be advantageous to combine S1 and S2 directly into athird data volume. This third data volume is typically isotropic ornear-isotropic with a resolution corresponding to the in-planeresolution of S1 and S2, thus reducing partial volume effects betweenslices (FIG. 7). S1 and S2 can first be registered into the samecoordinate system. If both scans are acquired during the same session(without moving the patient between scans), the image header informationis used to obtain the transformation matrix. Otherwise, a mutualinformation-based rigid registration is applied. The gray value for eachvoxel V of the third data volume is calculated as follows:

[0086] (1) determine the position in 3D space for V;

[0087] (2) determine the gray values in S1 and S2 at this position;

[0088] (3) interpolate the two gray values into a single gray value G;and

[0089] (4) assign G to V.

[0090] As an alternative to fusion of two or more imaging planes, datacan be obtained with isotropic or near isotropic resolution. This ispossible, for example, with spiral CT acquisition technique or novel MRIpulse sequence such as 3D acquisition techniques. Such 3D acquisitiontechniques include 3D Driven Equilibrium Transfer (DEFT), 3D FastSpin-Echo (FSE), 3D SSFP (Steady State Free Precession), 3D GradientEcho (GRE), 3D Spoiled Gradient Echo (SPGR), and 3D Flexible EquilibriumMR (FEMR) techniques. Images can be obtained using fat saturation orusing water selective excitation. Typically, an isotropic resolution of0.5×0.5×0.5 mm or less is desirable, although in select circumstances1.0×1.0×1.0 and even larger can yield adequate results. With nearisotropic resolution, the variation in voxel dimensions in one or moreplanes does not usually exceed 50%.

[0091] VII. In Vivo Measurement of Meniscal Dimensions

[0092] The dimensions and shape of a personalized interpositionalarthroplasty system can be determined by measuring a patient's meniscalshape and size and by evaluating the 3D geometry of the articularcartilage. Many osteoarthritis patients, however, have torn menisci,often times with only small or no meniscal remnants. In these patients,the shape of a personalized interpositional arthroplasty system can bedetermined by acquiring measurements of surrounding articular surfacesand structures.

[0093] In the knee, for example, a few measurements can be made on thefemoral and tibial bone in MR images of the diseased knee. For optimalfit, the shape of the superior surface of the implant should resemblethat of the superior surface of the respective meniscus. Measurements ofthe bones can help determine how well meniscal dimensions can bepredicted.

[0094]FIG. 8A illustrates an axial view of a meniscus 100. The meniscushas a maximum anterior-posterior distance 1, and a maximum mediallateral distance 2. In the knee, the meniscus compensates for ananterior horn and a posterior which each have a maximum length 3, 5 andwidth9, 11. The body itself has a maximum length 4 and width 10 whichare a function of the patient's anatomy. FIG. 8B illustrates a sagittalview of the meniscus in FIG. 8A. The meniscus 100 has a maximum height6, 8 which correlates to the maximum height of the anterior horn and theposterior horn. FIG. 8C illustrates a coronal view of the meniscus 100.From the coronal view it is apparent that the body has a maximum andminimum height.

[0095] Turning now to FIG. 9A, a sagittal view of a tibia 110 is shown.The tibia has a maximum anterior-posterior distance 12. FIG. 9Billustrates the coronal view of the tibia 110 shown in FIG. 9A. From thesagittal view it is apparent that the tibia has a maximum medial-lateraldistance 13, a maximum distance from the tibial spine to the edge 14,and a width 15.

[0096] The tibia mates with the femur 120, which is shown in a sagittalview in FIG. 10A. The femur has a maximum anterior-posterior distance 16and a maximum superior-interior distance 17. From the coronal view shownin FIG. 10B the maximum medial-lateral distance 18, the distance fromthe trochlea to the edge 19, and the width of the intercondylar notch 20is apparent.

[0097] A Pearson's correlation coefficient r can be obtained for avariety of measurements to assess how well one variable is expressed byanother variable. Suitable measurements include, for example, thefollowing measurements:

[0098] antero-posterior (AP) length of medial (lateral) meniscus with APlength of medial (lateral) femoral condyle;

[0099] AP length of medial (lateral) meniscus with AP length of medial(lateral) tibial plateau;

[0100] medio-lateral (ML) width of medial (lateral) meniscus with MLwidth of medial (lateral) femoral condyle;

[0101] ML width of medial (lateral) meniscus with ML width of medial(lateral) tibial plateau;

[0102] Y coordinate of highest point of medial (lateral) meniscus with ycoordinate of highest point of medial (lateral) tibial spine;

[0103] X coordinate of medial (lateral) margin of medial (lateral)meniscus with x coordinate of medial (lateral) margin of medial(lateral) femoral condyle; and

[0104] X coordinate of medial (lateral) margin of medial (lateral)meniscus with x coordinate of medial (lateral) margin of medial(lateral) tibial plateau.

[0105] Examples of measurements obtained are summarized in TABLE 2CORRELATION BETWEEN MENISCAL DIMENSIONS AND DIMENSIONS OF FEMORAL ANDTIBIAL BONE Measurement Imaging Plane N Pearson's r AP Length: medialmeniscus - medial Sagittal 23 0.74 femoral condyle AP Length: lateralmeniscus - lateral Sagittal 24 0.73 femoral condyle AP Length: medialmeniscus - medial Sagittal 23 0.79 tibial plateau AP Length: lateralmeniscus - lateral Sagittal 24 0.27 tibial plateau ML Width: menisci -femur Coronal 12 0.91 ML Width: menisci - tibia Coronal 12 0.92 MLWidth: menisci - medial femoral Coronal 12 0.81 condyle ML Width:menisci - lateral femoral Coronal 12 0.65 condyle ML Width: menisci -medial tibial Coronal 12 0.86 plateau ML Width: menisci - lateral tibialCoronal 12 0.48 plateau ML Width: medial meniscus - medial Coronal 120.95 femoral condyle ML Width: lateral meniscus - lateral Coronal 120.45 femoral condyle ML Width: medial meniscus - medial Coronal 12 0.69tibial plateau

[0106] TABLE 2 CORRELATION BETWEEN MENISCAL DIMENSIONS AND DIMENSIONS OFFEMORAL AND TIBIAL BONE Measurement Imaging Plane N Pearson's r MLWidth: lateral meniscus - lateral Coronal 12 0.34 tibial plateau MLLength: medial meniscus - lateral Coronal 12 0.12 meniscus MeniscalHeight: medial meniscus - Coronal 12 0.01 lateral meniscus MeniscalHeight: Medial meniscal Coronal 12 0.22 height - medial femoral heightMeniscal Height: Lateral meniscal Coronal 12 0.22 height - lateralfemoral height Meniscal Height: Medial meniscal Coronal 12 0.55 height -medial tibial height Meniscal Height: Lateral meniscal Coronal 12 0.17height - lateral tibial height Highest Point (y coordinate): medialCoronal 12 0.99 meniscus - medial tibial spine Highest Point (ycoordinate): lateral Coronal 12 0.90 meniscus - lateral tibial spineMedial margin (x-coordinate): medial Coronal 12 1.00 meniscus - femoralcondyle Lateral margin (x-coordinate): lateral Coronal 12 1.00meniscus - lateral femoral condyle Medial Margin (x-coordinate): medialCoronal 12 1.00 meniscus - medial tibial plateau Lateral Margin(x-coordinate): lateral Coronal 12 1.00 meniscus - lateral tibialplateau

[0107] The Pearsons' coefficient determines the relationship between twosizes that are measured. The higher the correlation, the better therelationship between two measurements. From the data in TABLE 2, itbecomes evident that, in the knee, the AP length of both medial andlateral menisci can be predicted well by measuring the length of therespective femoral condyle. For the medial meniscus, the length of themedial tibial plateau can also be used. The ML width of the medialfemoral condyle is a good predictor for the width of the medialmeniscus. The height of the medial and lateral tibial spines correlateswell with the height of the respective menisci. Correlations between MLwidth of the lateral meniscus and width of the lateral femoral condyleand tibial spine are lower due to a high variability of the most lateralpoint of the lateral meniscus. As opposed to these outermost points ofthe lateral meniscus, the main margins correlate very well with themargins of the tibia and femur. This is also the case for the medialmeniscus. Consequently, the outer margins of medial and lateral meniscican be determined.

[0108] These results show that meniscal dimensions can be predicted in areliable fashion by measuring bony landmarks in MR images. Where thePearson's coefficient is high (e.g., close to 1), the two measurementscan, in effect, be used interchangeably to represent the measurementdesired. Where the Pearson's coefficient is low (e.g., 0.34), acorrection factor may be applied to the measurement. The measurement ascorrected may then equal or approximate the corresponding measurement.In some instances, use of a correction factor may not be feasible ordesired. In that instance, other approaches, such as logistic regressionand multivariate analysis, can be used as an alternative withoutdeparting from the scope of the invention.

[0109] A person of skill in the art will appreciate that while this datahas been presented with respect to the meniscus in the knee andmeasurement of knee anatomy relative thereto, similar results wouldoccur in other joints within a body as well. Further, it is anticipatedthat a library of measurements can be created, for example forgenerating one or more correlation factors that can be used for aparticular joint. For example, a single correlation factor can begenerated using a plurality of measurements on different subjects.

[0110] Alternatively, a plurality of correlation factors can begenerated based on, for example, joint assessed, size, weight, body massindex, age, sex of a patient, ethnic background. In this scenario, apatient seeking treatment can be assessed. Measurements can be taken of,for example, the medial femoral condyle. The correlation factor for themedial femoral condyle in the patient can then be compared to acorrelation factor calculated based on samples wherein the samplepatients had the same, or were within a defined range for factors,including for example: size, weight, age and sex.

[0111] VIII. Surface Digitization

[0112] Digitized surface data from menisci of cadaveric specimens forgeneration of a generic meniscal model can be acquired using a TitaniumFaroArm® coordinate measurement machine (CMM) (FARO Technologies Inc.,Lake Mary, Fla.).

[0113] IX. 3D Design Techniques for Anatomically Correct InterpositionalArthroplasty System

[0114] The design workflow for each implant can consist of a combinationof one or more of the following steps:

[0115] a. Fusion of the sagittal and coronal 3D SPGR or 2D or 3D FSEdata or other sequences for a joint;

[0116] b. Segmentation of point data from the cartilage surface of ajoint;

[0117] c. Fusion of the sagittal and coronal 2D or 3D FSE or 2D SE dataor other sequences of a joint;

[0118] d. Segmentation point data of the superior meniscal surface;

[0119] e. Combination of cartilage surface data and meniscal surfacedata to serve as model for a surface of an implant;

[0120] f. Compression of a meniscal surface by factor ranging from 0.2to 0.99;

[0121] g. Conversion of point cloud data for a superior and an inferiorimplant surface into parametric surface data; and

[0122] h. Cutting of parametric surface data sets to determine exactshape of implant.

[0123] In many patients with advanced osteoarthritis, however, themeniscus is, to a great extent, depleted, and therefore cannot servedirectly as a template from which the superior implant surface can bederived.In these cases, dimensions of the remaining joint bone, can beused to adjust the size of a generic meniscal model, which can thenserve as a template for the implant.

[0124] X. Derivation of Implant Surfaces from Cartilage and HealthyMeniscal Surfaces

[0125] The superior surface of an implant can be modeled based on thesuperior meniscal surface and the joint cartilage surface in those areasthat are not covered by the meniscus. Therefore, after theslice-by-slice segmentation of the superior meniscal surface from the SEor FSE or other MRI images and the tibial cartilage surface from the 3DSPGR or FSE or other MRI images, both data sets will be combined (FIGS.11A-C). To determine the composite surface for the prosthesis, theintersection between the two surfaces is located. In the event that thetwo surfaces do not intersect in a particular slice, the intersectionbetween the tangential line through the central end of the meniscalsurface with the tibial surface will be calculated (FIG. 11A). Toaccount for natural compression of the elastic meniscus under load, itsheight can be adjusted, for example, to 60% of the original height (FIG.11B). For this purpose, each point on the meniscal surface is connectedto the closest point on the cartilage surface. The new point for theadjusted meniscal surface is chosen at 60% of the distance from thetibial cartilage surface.

[0126] As will be appreciated by those of skill in the art, a variety ofother adjustment ratios can be used without departing from the scope ofthe invention. Suitable adjustment ratios will vary depending on patientphysiology and desired degree of correction and include, for example,ratios that range from 0.2 to 1.5. The amount of height adjustment ofthe implant relative to the natural meniscus will vary depending uponthe material that the implant is manufactured from. For example, wherethe implant is manufactured from a material having a high degree ofelasticity, it may be desirable to use an adjustment greater than 1.Where the material has a low degree of elasticity, the adjustment islikely to approach 50%. The appropriate adjustment will also depend uponthe joint for which the implant is manufactured. Thus, for example, animplant manufactured for the knee using a material with a low degree ofelasticity can have an adjustment of between 50-70%, while an implantmanufactured for the shoulder also using a material with a low degree ofelasticity may have a desired adjustment of 60-80%. Persons of skill inthe art will appreciate that the correction factor for an implant willvary depending upon the target joint and the properties of the materialfrom which the implant is manufactured.

[0127] The adjustment ratio can also vary depending on the locationwithin a joint with a plurality of ratios possible for any given design.For example, in a knee joint, an adjustment ratio close to 0.8 can beused anteriorly, while an adjustment ratio close to 0.5 can be usedposteriorly. Additionally, more adjustment ratios can be selected suchthat the adjustment ratio gradually changes, for example, anteriorly,depending on the anticipated biomechanics of the joint. Changes can alsobe made to the adjustment ratio as a result of patient specificparameters such as age, sex, weight, ethnicity, and activity level. Theadjustment ratio can be selected in order to achieve an optimalbiomechanical or functional result. In vitro cadaveric testing,constraint testing, testing of contact surface, fatigue testing androbotic testing can, for example, be used for determining the optimaladjustment ratio(s) for an implant.

[0128] Finally, to determine the shape of the superior surface of theimplant, the compressed meniscal surface can be combined with theportion of the tibial cartilage surface that is not covered by themeniscus. The shape of, for example, an inferior surface of the implantcan be derived from the entire cartilage surface (FIG. 11C) or thesubchondral bone surface. The latter can be used, for example, if thereis significant eburnation of the joint and most of the cartilage hasbeen lost.

[0129] XI. Derivation of Superior Implant Surface in Case of DamagedMeniscus

[0130] In patients with a damaged or degenerated meniscus or those thathad a prior meniscectomy, the meniscal surface cannot be used as atemplate for an implant surface as described above. In these cases, ageneric meniscal model can be used to design the desired implantsurface.

[0131] The generic meniscal model can be generated from data that is,for example, collected from cadaveric femoral specimens using a TitaniumFaroArm as described above. Alternatively, a laser scanning device or anoptical device can be used. In this instance, meniscal surface data canbe digitized, for example, from ten frozen cadaveric tibial specimens.All surface data sets obtained can then be matched for size differencesusing, for example, an affine surface registration scheme. The matchedsurface points after registration can then be merged into a single pointcloud. A generic meniscal surface, S_(g), can be fitted through a pointcloud using a least-squares optimization, resulting in a “mean” surfaceof the ten specimens.

[0132] Typically, dimensions of healthy menisci correlate well withdimensions of bony landmarks. Therefore, measurements of bony landmarksin an MRI can be used to reconstruct the dimensions of the healthymeniscus (see, e.g., TABLE 2, above). The antero-posterior length L willbe calculated from the length of the femoral condyle. For determiningmedio-lateral meniscal width W, we can use the position of the medialmargin of the tibia for the medial meniscus and the lateral tibialmargin for the lateral meniscus. The height H can be derived from thehighest point of the tibial spine.

[0133] Once the values L, W, and H have been determined, S_(g) can bedeformed accordingly. Each point P in S_(g) with the coordinates (x, y,z) can be transformed into a new point P′ using Equation 4:$\begin{matrix}{{P^{\prime} = {\left( {x^{\prime},y^{\prime},z^{\prime}} \right) = \left( {{\frac{L}{L_{g}} \cdot x},{\frac{W}{W_{g}} \cdot y},{\frac{H}{H_{g}} \cdot z}} \right)}},} & \left\lbrack {{Eq}.\quad 4} \right\rbrack\end{matrix}$

[0134] where L_(g), W_(g), and H_(g) are the respective dimensions ofS_(g). The transformed points P′ can form the meniscal surface S thatwill be used as a template for designing the superior implant surface asdescribed in the previous section.

[0135] XII. Final Steps of Implant Design

[0136] The first and second implant surfaces derived from an MR image,as described above, consist of point clouds. The point clouds can beconverted into a data format that then can be manipulated in, forexample, a CAD system. The Surface Patch function in the surfacemodeling program Rhinoceros can be used to approximate a smooth surfacepatch to the point cloud data (FIG. 12). This surface can then beexported in the IGES format to be read by the CAD software. Othersoftware programs can be used without departing from the scope of theinvention. For example, Pro/Engineer, Solid Edge, Alibre and IronCAD arealso suitable programs.

[0137] Using the CAD software SolidWorks, the superior and inferiorsurfaces can be combined into one design model. Both surfaces can beclipped using the outer meniscal edge as a margin (FIG. 11).

[0138] From this information, joint implants can be designed that takeinto consideration the dimensions. FIGS. 13A and B are views of a jointimplant suitable for use on a condyle of the femur. These views areshown from the inferior and superior surface viewpoints. The surfaces,edges and height of the implant can be adjusted to account for themeasurements taken to achieve an implant with an optimal patient fit.FIG. 14 is a view of an implant suitable for placement in a joint kneeand placed on a portion of the tibial plateau. FIGS. 15A-D are views ofan implant suitable for the hip. These implants can also be designed sothat the surfaces, edges and height of the implants can be adjusted toaccount for the measurements taken as well as the patient specificcriteria, as appropriate or desirable.

[0139] XIII. Accuracy of 3D Imaging and 3D Sizing Techniques forDeriving 3D Shape of Implant

[0140] In order to determine how much the predicted meniscal surface,calculated from the generic model, differs from the true shape of themeniscus, healthy volunteers can be examined. Suitable spiral CT, alsowith intravenous or intra-articular contrast enhancement, or MRI imagescan be acquired, from which medial and lateral menisci can then beextracted using live wire segmentation, or other suitable mechanisms.Furthermore, the generic models for the medial and lateral meniscus canbe fitted as described above. For each subject, the medial and lateralmeniscus that was segmented from the MRI can be compared to the fittedmodels as follows:

[0141] 1. For each point P=(x,y,z) in the segmented data set choose theclosest point P₁=(x₁,y₁,z₁) from the fitted model with z₁≧z and the twoclosest points P₂=(x₂,y₂,z₂) and P₃=(x₃,y₃,z₃) with z₂,z₃≦z.

[0142] 2. The point P is projected orthogonally onto the plane definedby P₁, P₂ and P₃. The projected point P′ is given by:$P^{\prime} = {P - \frac{\left( {{P - P_{1}},n} \right)}{\left( {n,n} \right)}}$

[0143]  where n is the normal to the plane and (•, •) denotes the dotproduct.

[0144] 3. Calculate the distance d, between P and the plane, given by

d ₁ =∥P′−P∥.  i.

[0145] 4. Repeat 1-3 with P₁=(x₁,y₁,z₁) such that z₁≦z and P₂=(x₂,y₂,z₂)and P₃=(x₃,y₃,z₃) such that z₂,z₃≧z, resulting in d₂.

[0146] 5. Calculate the mean distance for P: d(P)=(d₁+d₂)/2.

[0147] 6. Calculate the total distance measure D over all points in thesegmented data set: $D = {\sum\limits_{P}{{(P)}.}}$

[0148] The total distance measure D depends on the relative position ofthe segmented MRI data and the fitted model in the coordinate system.This relative position can be optimized to minimize D by adjusting therigid body transformation T that positions the model in an iterativeregistration process based on the iterative closest point algorithm,using D(T) as a cost function.

[0149] Typically, it is anticipated that the accuracy of this fittingapproach is sufficient if the average distance D/n, where n is thenumber of points in the segmented data, is below 1.5 mm.

[0150] The foregoing description of embodiments of the present inventionhas been provided for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations will beapparent to the practitioner skilled in the art. The embodiments werechosen and described in order to best explain the principles of theinvention and its practical application, thereby enabling others skilledin the art to understand the invention and the various embodiments andwith various modifications that are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the following claims and equivalents.

What is claimed:
 1. A method to treat a defect in a joint comprising:obtaining an image of a joint; and generating at least one of athickness map and a curvature map.
 2. The method of claim 1 furthercomprising one or more of the steps of: pre-processing the imageobtained using a non-linear diffusion filter; assigning a list offeatures to each oriented edge between at least two pixel boundaries;converting the features into cost values; and calculating a single costvalue.
 3. The method of claim 2 further comprising the step of:determining the likelihood of a cost value being a part of a cartilageboundary.
 4. The method of claim 1 or claim 3 further comprising thestep of: determining a contour of a cartilage object by selecting atleast a first pixel and a second pixel.
 5. The method of claim 4 whereinthe first pixel and the second pixel are automatically selected.
 6. Themethod of claim 4 wherein the first pixel and the second pixel areselected by an operator.
 7. The method of claim 1 further comprising thestep of calculating cartilage thickness.
 8. The method of claim 7wherein the step of calculating cartilage thickness is performed using a3D Euclidean Transform.
 9. The method of claim 7 wherein the step ofcalculating cartilage thickness is performed by decomposing thecalculation into a series of three one-dimensional transformations. 10.The method of claim 9 further wherein the one-dimensional transforms aresquared to obtain a set of distances.
 11. The method of claim 8 whereina thickness of cartilage for a point on an outer cartilage surface iscalculated based on the square root of S_(abc).
 12. The method of claim1 further wherein an implant is designed from the generated thicknessmap.
 13. The method of claim 1 wherein the defect is a result of atleast one of cartilage disease, bone damage, trauma, and degeneration.14. The method of claim 9, 11, or 12 wherein the thickness is a measuredthickness and is used to design an implant for treating the defect inthe joint.
 15. The method of claim 14 wherein the measured thickness isadjusted on at least a portion of the implant based on a quality of amaterial selected to manufacture the implant.
 16. The method of claim 15wherein the measured thickness is adjusted to a final implant thicknesson at least a portion of the implant by a factor of from 0.2 to 1.5 ofthe measured thickness.
 17. An implant suitable for treating a defect ina joint wherein the implant is designed by: obtaining an image of ajoint; and generating at least one of a thickness map and a curvaturemap.
 18. The method of claim 17 further comprising one or more of thesteps of: processing the image obtained using a non-linear diffusionfilter; assigning a list of features to each oriented edge between atleast two pixel boundaries; converting the features into cost values;and calculating a single cost value.
 19. The method of claim 18 furthercomprising the step of: determining the likelihood of a cost value beinga part of a cartilage boundary.
 20. The method of claim 17 or claim 18further comprising the step of: determining a contour of a cartilageobject by selecting at least a first pixel and a second pixel.
 21. Themethod of claim 20 wherein the first pixel and the second pixel areautomatically selected.
 22. The method of claim 20 wherein the firstpixel and the second pixel are selected by an operator.
 23. The methodof claim 17 further comprising the step of calculating cartilagethickness.
 24. The method of claim 23 wherein the step of calculatingcartilage thickness is performed using a 3D Euclidean Transform.
 25. Themethod of claim 23 wherein the step of calculating cartilage thicknessis performed by decomposing the calculation into a series of threeone-dimensional transformations.
 26. The method of claim 25 furtherwherein the one-dimensional transforms are squared to obtain a set ofdistances.
 27. The method of claim 24 wherein a thickness of cartilagefor a point on an outer cartilage surface is calculated based on thesquare root of S_(abc).
 28. The method of claim 17 wherein the defect isa result of at least one of cartilage disease, bone damage, trauma, anddegeneration.
 29. The method of claim 25, 27 or 28 wherein the thicknessis a measured thickness and is used to design an implant for treatingthe defect in the joint.
 30. The method of claim 29 wherein the measuredthickness is adjusted on at least a portion of the implant based on aquality of a material selected to manufacture the implant.
 31. Themethod of claim 29 wherein the measured thickness is adjusted to a finalimplant thickness on at least a portion of the implant by a factor offrom 0.2 to 1.5 of the measured thickness.
 32. A method to treat adefect in a joint comprising: obtaining an image of a joint; processingthe image obtained using a non-linear diffusion filter; and generating acartilage curve.
 33. The method of claim 32 further comprising the stepsof: fitting a local bi-cubic surface path to the cartilage curve. 34.The method of claim 32 wherein the bi-cubic surface patch isautomatically selected.
 35. The method of claim 32 wherein the bi-cubicsurface patch is selected by an operator.
 36. The method of claim 32further comprising the step of calculating cartilage thickness.
 37. Themethod of claim 36 wherein the step of calculating cartilage thicknessis performed using a 3D Euclidean Transform.
 38. The method of claim 36wherein the step of calculating cartilage thickness is performed bydecomposing the calculation into a series of three one-dimensionaltransformations.
 39. The method of claim 38 further wherein theone-dimensional transforms are squared to obtain a set of distances. 40.The method of claim 37 wherein a thickness of cartilage for a point onan outer cartilage surface is calculated based on the square root ofS_(abc).
 41. The method of claim 32 further wherein an implant isdesigned from the cartilage curve.
 42. The method of claim 38, 40 or 41wherein the thickness is a measured thickness and is used to design animplant for treating the defect in the joint.
 43. The method of claim 42wherein the measured thickness is adjusted on at least a portion of theimplant based on a quality of a material selected to manufacture theimplant.
 44. The method of claim 42 wherein the measured thickness isadjusted to a final implant thickness on at least a portion of theimplant by a factor of from 0.2 to 1.5 of the measured thickness.
 45. Animplant for correcting a defect in a joint wherein the implant size isdetermined by estimating meniscal dimensions based on measurements of atleast one of cartilage and bone landmarks within the joint.
 46. Theimplant of claim 45 wherein the joint is a knee joint.
 47. The implantof claim 46 wherein the measurement is selected from the groupconsisting of: a length of a medial meniscus; a length of a medialfemoral condyle; a length of a lateral meniscus; a length of a lateralfemoral condyle; a length of a medial tibial plateau; a length of alateral tibial plateau; a width of a medial meniscus; a width of amedial femoral condyle; a width of a lateral meniscus; a width of alateral femoral condyle; a width of a medial tibial plateau; a width ofa lateral tibial plateau; a highest point of a medial meniscus; ahighest point of a medial tibial spine; a highest point of a lateralmeniscus; a highest point of a lateral tibial spine; a highest point ofa femoral condyle; and a highest point of a lateral femoral condyle,cartilage thickness and cartilage curvature and 3D cartilage shape. 48.The implant of claim 45 wherein the joint is an ankle joint.
 49. Theimplant of claim 48 wherein the measurement is selected from the groupconsisting of: the diameter of a talus, the length of a talus, the widthof a talus, the curvature of a talus, the cartilage thickness of atalus, the subchondral bone thickness of a talus, the diameter of acalcaneus, the length of a calcaneus, the width of a calcaneus, thecurvature of a calcaneus, the cartilage thickness of a calcaneus, thesubchondral bone thickness of a calcaneus.
 50. The implant of claim 45wherein the joint is a hip joint.
 51. The implant of claim 50 whereinthe measurement is selected from the group consisting of themediolateral diameter of an acetabular fossa, the anteroposteriordiameter of the acetabular fossa, the superoinferior diameter of theacetabular fossa, the curvature of the acetabular fossa anteriorly,posteriorly, superiorly, inferiorly, medially or laterally, thethickness of the articular cartilage of the acetabular fossa anteriorly,posteriorly, superiorly, inferiorly, medially or laterally, thethickness of the subchondral bone of the acetabular fossa anteriorly,posteriorly, superiorly, inferiorly, medially or laterally, themediolateral diameter of a femoral head, the anteroposterior diameter ofthe femoral head, the superoinferior diameter of the femoral head, thecurvature of the femoral head anteriorly, posteriorly, superiorly,inferiorly, medially or laterally, the thickness of the articularcartilage of the femoral head anteriorly, posteriorly, superiorly,inferiorly, medially or laterally, the thickness of the subchondral boneof the femoral head anteriorly, posteriorly, superiorly, inferiorly,medially or laterally.
 52. The implant of claim 45 wherein the joint isa shoulder joint.
 53. The implant of claim 52 wherein the measurement isselected from the group consisting of the mediolateral diameter of aglenoid fossa, the anteroposterior diameter of the glenoid fossa, thesuperoinferior diameter of the glenoid fossa, the curvature of theglenoid fossa anteriorly, posteriorly, superiorly, inferiorly, mediallyor laterally, the thickness of the articular cartilage of the glenoidfossa anteriorly, posteriorly, superiorly, inferiorly, medially orlaterally, the thickness of the subchondral bone of the glenoid fossaanteriorly, posteriorly, superiorly, inferiorly, medially or laterally,the mediolateral diameter of a humeral head, the anteroposteriordiameter of the humeral head, the superoinferior diameter of the humeralhead, the curvature of the humeral head anteriorly, posteriorly,superiorly, inferiorly, medially or laterally, the thickness of thearticular cartilage of the humeral head anteriorly, posteriorly,superiorly, inferiorly, medially or laterally, the thickness of thesubchondral bone of the humeral head anteriorly, posteriorly,superiorly, inferiorly, medially or laterally.
 54. The implant of claim45 wherein the joint is an elbow joint.
 55. The implant of claim 54wherein the measurement is selected from the group consisting of thediameter of a distal humerus, the depth of a distal humerus, the widthof a distal humerus, the curvature of a distal humerus, the cartilagethickness of a distal humerus, the subchondral bone thickness of adistal humerus, the diameter of a radius, the depth of a radius, thewidth of a radius, the curvature of a radius, the cartilage thickness ofa radius, the subchondral bone thickness of a radius, the diameter of anulna, the depth of an ulna, the width of an ulna, the curvature of anulna, the cartilage thickness of an ulna, the subchondral bone thicknessof an ulna
 56. The implant of claim 45 wherein the joint is a wristjoint.
 57. The implant of claim 56 wherein the measurement is selectedfrom the group consisting of the diameter of a radius, the depth of aradius, the width of a radius, the curvature of a radius, the cartilagethickness of a radius, the subchondral bone thickness of a radius, thediameter of an ulna, the depth of an ulna, the width of an ulna, thecurvature of an ulna, the cartilage thickness of an ulna, thesubchondral bone thickness of an ulna, the diameter of a proximal carpalrow, the depth of a proximal carpal row, the width of a proximal carpalrow, the curvature of a proximal carpal row, the cartilage thickness ofa proximal carpal row, the subchondral bone thickness of a proximalcarpal row, the diameter of a scaphoid or lunate, the depth of ascaphoid or lunate, the width of a scaphoid or lunate, the curvature ofa scaphoid or lunate, the cartilage thickness of a scaphoid or lunate,the subchondral bone thickness of a scaphoid or lunate, the diameter ofa triangular fibrocartilage, the depth of a triangular fibrocartilage,the width of a triangular fibrocartilage, the curvature of a triangularfibrocartilage, the thickness of a triangular fibrocartilage.
 58. Theimplant of claim 45 wherein the joint is a finger joint.
 59. The implantof claim 59 wherein the measurement is selected from the groupconsisting of the depth of a phalanx or metacarpal, the width of aphalanx or metacarpal, the diameter of a phalanx or metacarpal, thecurvature of a phalanx or metacarpal, the cartilage thickness of aphalanx or metacarpal, the subchondral bone thickness of a phalanx ormetacarpal.
 60. The implant of claim 45 wherein the joint is in thespine.
 61. The implant of claim 60 wherein the measurement is selectedfrom the group consisting of the anteroposterior vertebral dimension,the mediolateral vertebral dimension, the height of the vertebral bodyanteriorly, centrally or posteriorly, the diameter of the pedicle(s),the width of the pedicle(s), the length of the pedicle(s), the diameteror radius of a facet joint(s), the volume of a facet joint(s), the 3Dshape of a facet joint(s), the curvature of a facet joint(s), thedimensions of the posterior elements, the dimensions of the spinalcanal, the 3D shape of the vertebral body.
 62. An implant for treating ajoint wherein the implant size is determined by estimating articulardimensions based on measurements of cartilage or bone landmarks withinthe joint.
 63. A technique for designing an anatomically correctinterpositional arthroplasty system for a joint comprising the followingsteps: obtaining data of a cartilage or bone surface of the joint;obtaining data of one or more meniscal surface(s); combination ofcartilage or bone surface data and meniscal surface data.
 64. The methodof claim 63 wherein data for existing bone joints is used to adjust thesize of the meniscal model.
 65. A method to treat a defect in a jointcomprising: obtaining an image of a joint; and measuring at least one ofcurvature and thickness.
 66. The method of claim 65 further comprisingone or more of the steps of: pre-processing the image obtained using anon-linear diffusion filter; assigning a list of features to eachoriented edge between at least two pixel boundaries; converting thefeatures into cost values; and calculating a single cost value.
 67. Themethod of claim 66 further comprising the step of: determining thelikelihood of a cost value being a part of a cartilage boundary.
 68. Themethod of claim 65 or claim 67 further comprising the step of:determining a contour of a cartilage object by selecting at least afirst pixel and a second pixel.
 69. The method of claim 68 wherein thefirst pixel and the second pixel are automatically selected.
 70. Themethod of claim 68 wherein the first pixel and the second pixel areselected by an operator.
 71. The method of claim 65 further wherein thestep of measuring thickness is performed by calculating cartilagethickness.
 72. The method of claim 71 wherein the step of calculatingcartilage thickness is performed using a 3D Euclidean Transform.
 73. Themethod of claim 71 wherein the step of calculating cartilage thicknessis performed by decomposing the calculation into a series of threeone-dimensional transformations.
 74. The method of claim 73 furtherwherein the one-dimensional transforms are squared to obtain a set ofdistances.
 75. The method of claim 72 wherein a thickness of cartilagefor a point on an outer cartilage surface is calculated based on thesquare root of S_(abc).
 76. The method of claim 65 further wherein animplant is designed from the measurement of at least one of curvatureand thickness.
 77. The method of claim 65 wherein the defect is a resultof at least one of cartilage disease, bone damage, trauma, anddegeneration.
 78. The method of claim 73, 75 or 76 wherein the thicknessis a measured thickness and is used to design an implant for treatingthe defect in the joint.
 79. The method of claim 78 wherein the measuredthickness is adjusted on at least a portion of the implant based on aquality of a material selected to manufacture the implant.
 80. Themethod of claim 79 wherein the measured thickness is adjusted to a finalimplant thickness on at least a portion of the implant by a factor offrom 0.2 to 1.5 of the measured thickness.
 81. An implant suitable fortreating a defect in a joint wherein the implant is designed by:obtaining an image of a joint; and measuring at least one of curvatureand thickness.
 82. The method of claim 81 further comprising one or moreof the steps of: processing the image obtained using a non-lineardiffusion filter; assigning a list of features to each oriented edgebetween at least two pixel boundaries; converting the features into costvalues; and calculating a single cost value.
 83. The method of claim 82further comprising the step of: determining the likelihood of a costvalue being a part of a cartilage boundary.
 84. The method of claim 81or claim 82 further comprising the step of: determining a contour of acartilage object by selecting at least a first pixel and a second pixel.85. The method of claim 84 wherein the first pixel and the second pixelare automatically selected.
 86. The method of claim 84 wherein the firstpixel and the second pixel are selected by an operator.
 87. The methodof claim 81 further comprising the step of calculating cartilagethickness.
 88. The method of claim 87 wherein the step of calculatingcartilage thickness is performed using a 3D Euclidean Transform.
 89. Themethod of claim 87 wherein the step of calculating cartilage thicknessis performed by decomposing the calculation into a series of threeone-dimensional transformations.
 90. The method of claim 89 furtherwherein the one-dimensional transforms are squared to obtain a set ofdistances.
 91. The method of claim 88 wherein a thickness of cartilagefor a point on an outer cartilage surface is calculated based on thesquare root of S_(abc).
 92. The method of claim 81 wherein the defect isa result of at least one of cartilage disease, bone damage, trauma, anddegeneration.
 93. The method of claim 89, 91 or 92 wherein the thicknessis a measured thickness and is used to design an implant for treatingthe defect in the joint.
 94. The method of claim 93 wherein the measuredthickness is adjusted on at least a portion of the implant based on aquality of a material selected to manufacture the implant.
 95. Themethod of claim 93 wherein the measured thickness is adjusted to a finalimplant thickness on at least a portion of the implant by a factor offrom 0.2 to 1.5 of the measured thickness.
 96. An implant for correctinga defect in a joint wherein the implant size is determined by estimatingmeniscal dimensions based on measurements of at least one of a thicknessand curvature.
 97. An implant for correcting a defect in a joint whereinthe implant size is determined by estimating meniscal dimensions basedon measurements of at least one of a thickness map and a curvature map.